The present invention relates to a method for synthesizing 2-fluoro-2-deoxy-D-glucose with an [.sup.18 F]fluoride ion prepared without addition of a carrier to produce a radiopharmaceutical for Positron Emission Tomography (PET). More particularly, the present invention relates to a method for making 2-[.sup.18 F]fluoro-2-deoxy-D-glucose involving the replacement of the trifluoromethanesulfonyl group (triflate) with an [.sup.18 F]fluoride ion in 1,3,4,6-tetra-O-acetyl-2-triflate-.beta.-D-mannopyranose, where a phase-transfer reagent (PTR) is used in the form of a dibenzo substituted aminopolyether alkali metal complex (Kryptofix 222BB).
Prior to the present invention, various procedures were used for making 2-[.sup.18 F]fluoro-2-deoxy-D-glucose or "[.sup.18 F]2FDG", which is the most widely used radiopharmaceutical for Positron Emission Tomography (PET). Considerable effort has been expended in the development and refinement of such procedures. Because of its decay energy, (0.64 MEV) the [.sup.18 F] fluoride ion allows the highest inherent resolution during PET measurements and has a relatively convenient half life of 109.7 min. The following equation illustrates the preferred procedure for making [.sup.18 F]2FDG: ##STR1## where AcO is acetate.
One method of synthesizing [.sup.18 F]2FDG by the above procedure is shown by Hamacher et al., Journal of Nuclear Medicine, 27:235-238, (1986). Hamacher et al. employ an aminopolyether [Kryptofix 222 or "K222"]-potassium carbonate complex as a phase-transfer reagent for [.sup.18 F]fluoride. An additional procedure for making [.sup.18 F]2FDG is shown by Brodack et al., Applied Radiation and Isotope, Volume 39, No. 7, pages 699-703 (1988) involving the employment of a tetrabutylammonium hydroxide as a phase-transfer reagent in place of the aminopolyether potassium complex of Hamacher et al.
Although cryptands, such as Kryptofix 222 having the formula, ##STR2## have been found useful as phase transfer reagents, cryptands also have been found to be toxic. As a result their use in producing radiopharmaceuticals for PET applications has to be carefully monitored to assure their absence in the final product. Means for enhancing the detection and removal of cryptands from the product stream are therefore constantly being sought.